The idea is to suggest to people that Google has let them down while Bing, which is Microsoft's search engine, is waiting to give them a hand up. "Have you been Scroogled?" it screams at us, "Try Bing."

According to Microsoft, Google buries information in its terms and conditions that it does not want innocent shoppers to see. This information is why it looks like shopping results are sorted by relevance when they are actually sorted by how much retailers pay for them.

"They Scroogle you," says Microsoft, "by defining relevance as how much they're getting paid." We are advised, in the ad, that Bing offers you "an honest search".

It says that Google has changed, but has not kept its users up to date with the changes that it has made.

"Google now wants to break the rules that made it a trusted brand. They argue that the difference between answers and ads is shrinking. 'After all,' they recently said, 'ads are just more answers to users’ queries,'" says the Bing team in the post.

"Shoppers visit the site they have used for years, conduct what they think is a 'search,' and get a set of rankings that look like the objective results Google delivers elsewhere. Meanwhile, the lawyers at Google are now calling it a 'listing'. Consumers are potentially getting a raw deal because 'relevance' is now influenced by how much Google is getting paid, not just by things that matter to shoppers."

We asked Google to respond, and it said, "We made the transition to Google Shopping to improve the shopping experience for our users. We believe that having a commercial relationship with merchants will encourage them to keep their product information fresh and up to date."